When setting timing with a vacum advance distributor you pay no attention to the vacum advance right? Because under boost you will have no vacum? Had a guy tell me that making sure it is right he told me set the timing by the base time plus the sentrifical advance. Is that right thing for me to do?

thanks
newt-rod

 

is this true?

 

I am trying to find out need to know for myself.

thanks
newt-rod

 

You want to check total mechanical advance with vacuum advance disabled. You may also want to put a check valve in line with the vacuum canister to prevent it from seeing boost.

 

thanks. So the vacum advance will not work under boost right?

thanks
newt-rod

 

vacuum advance works under vacuum. Highest advance at idle if you aren't using a ported vacuum source, as you open the throttle the vacuum signal decreases the vacuum advance will decrease along with it. At WOT you should have no advance from the vacuum mechanism in a N/A application. I can't really say what will happen if you put boost on it with no check valve. Corky Bell talks about using the vacuum advance under boost to retard the timing.

 

To be safe, if you want to keep the vac advance hooked up, check your total timing using some sort of regulated pressure supply (a bike pump and some vac tube) with the motor at the RPM your full advance comes in and the boost you plan on running - that should tell you what's happening under boost.

It's hard to say what a plain ol' distributor will do with boost on the cannister - I'm not sure if the linkage is designed to go "backwards" in that manner. If it is, you'd see retard, but.....

Honestly, I'd disconnect it altogether and disable it - all it will do is get you slightly better economy on decel and keep the chambers from loading up (on decel)......probably not worth chasing around and trying to make it do something it wasn't designed for.